In conventional sheet-type electrode devices for measuring ion concentrations, as disclosed in Japanese Patent Application Laid-Open No. Sho 63-225164, a thin film ion-selective responsive membrane is formed on an upper surface of an insulating support layer. The membrane is formed by dripping an ion-selective responsive membrane paste, containing a solvent, upon the upper surface of the insulating support layer. The solvent may be polyvinyl chloride resin powders, to which the insulating support layer is soluble, and an ion-responsive substance.
In such prior art sheet-type electrodes, the ion-selective responsive membrane is capable of sealing against the support layer and being formed within a short time. This advantage allows mass production, but problems have occurred.
Due to the fact that the sample to be measured is liquid in many cases, the responsive membrane becomes swollen and deteriorates after repeated measurements. The surface of the responsive membrane is wiped with materials such as gauze when the membrane is used as a sheet-type electrode to measure ions. Wiping the surface of the responsive membrane also causes the membrane to become deformed or substantially worn when rubbed hard.
Attempts have been made to strengthen the ion-selective responsive membrane by adding reinforcing materials, such as a nylon mesh or other inorganic material, in the formation of the responsive membrane. This addition of a reinforcing material to the responsive membrane has resulted in the reinforcing material projecting from the surface of the responsive membrane while the responsive membrane is being used. These projections cause insulating fractures, and thereby reduce accuracy.